1. Field of the Invention
The invention relates to a bedding mat for supporting an exhaust gas catalyst in a metallic catalyst housing. This catalyst is used for purifying the exhaust gases of motor vehicles. The bedding mat is arranged along the periphery of the ceramic body supporting an exhaust gas catalyst, and seals the annular gap between the ceramic carrier body and the catalyst housing, which consists of a metallic material. This bedding mat is expected to permit a safe and shock-free bedding of the ceramic carrier body. It also has to compensate for any change in the width of the annular gap to be sealed when the metallic housing of the catalyst expands due to the operating temperature, which is determined by the combustion gases. Furthermore, the bedding mat forms a heat insulation layer on the inner wall of the catalyst housing, and reduces the sound noise of the flowing exhaust gases, which are transmitted to the outside.
2. The Prior Art
A mechanically solidified bedding mat made of textured yarns is known from Patent WO 00/36284. The yarns are fixed in the flat structure under tensile stress by quilted seams. The quilted seams are produced with a sewing thread whose thermal stability is lower than the operating temperature of the bedding mat. The quilted seams are destroyed when the bedding mat is heated. Deformation energy on the textured yarn is thereby released, and the volume of the bedding mat increases. The expansion property of the bedding mat results from laying the textured yarns under tensile stress as they are being processed further to produce a mat. This tensile stress is mechanically fixed, and the possibilities available for manufacturing and conditioning these mats using this technique are restricted.
A bedding mat known from German Patent DE-U 93 11 571 consists of short inorganic fibers, an organic binding agent, as well as particle-shaped inclusions made of an expanding material such as, for example mica or vermiculite, which expands when acted upon by heat, and causes the volume of the bedding mat to increase at the operating temperature. The inorganic fibers included in the binding agent consist of ceramic staple fibers or crushed SiO2-filaments, with an average length of a few millimeters. A bedding mat with short inorganic fibers exhibits a tendency to erosion and wear. Both the fibers and the particulate expanding material are discharged with the flowing combustion gases, with the result that the seal of the annular gap deteriorates, and erosion increases. The use of a fiber material with longer filaments increases the risk that fibers are blown out, although to a lesser degree. However, the formation of bridges and crosslinking of the filaments obstruct the expansion of the mat, and the effect of the expanding material does not fully come to bear.
The invention provides a bedding mat for the purpose specified above which is blowout-proof, and has high expansion capability that is improved versus the prior art mats specified above. Furthermore, conventional methods of textile processing are to be applicable for producing the mat according to the invention.
It is an object of the invention to provide a bedding mat for supporting an exhaust gas catalyst in a metallic catalyst housing that is used for purifying the exhaust gases of motor vehicles. This bedding mat is made from the following materials:
1. A yarn that is processed to a flat textile structure, the yarn consisting of voluminous, thermally stable filaments that are aligned in parallel and bundled to form the yarn, and a casing for the yarn that decomposes upon heating; and
2. an edge protection made of thermally stable threads extending along the edges of the flat structure.